Add new column into Root to get the supported query args

DocumentsContract:
- Add @Public column Root#COLUMN_QUERY_ARGS
- Update java doc

DocumentsProvider:
- Update java doc

FileSystemProvider & ExternalStorageProvider
- Add supported query args into Roots

Bug: 121234248
Test: manual
Change-Id: Ia944200ee1a44d75c9ad683564218e3d0dcef885